Health Monitoring of Stress-Laminated Timber Bridges Assisted by a Hygro-Thermal Model for Wood Material

Stefania Fortino,Ludovic Fülöp,Petr Hradil,Antti Korkealaakso,Timo Tirkkonen,Hauke Burkart,Keijo Koski

doi:10.3390/app11010098

Abstract

Timber bridges are economical, easy to construct, use renewable material and can have a long service life, especially in Nordic climates. Nevertheless, durability of timber bridges has been a concern of designers and structural engineers because most of their load-carrying members are exposed to the external climate. In combination with certain temperatures, the moisture content (MC) accumulated in wood for long periods may cause conditions suitable for timber biodegradation. In addition, moisture induced cracks and deformations are often found in timber decks. This study shows how the long term monitoring of stress-laminated timber decks can be assisted by a recent multi-phase finite element model predicting the distribution of MC, relative humidity (RH) and temperature (T) in wood. The hygro-thermal monitoring data are collected from an earlier study of the Sørliveien Bridge in Norway and from a research on the new Tapiola Bridge in Finland. In both cases, the monitoring uses integrated humidity-temperature sensors which provide the RH and T in given locations of the deck. The numerical results show a good agreement with the measurements and allow analysing the MCs at the bottom of the decks that could be responsible of cracks and cupping deformations.

Highlights

Timber and engineered wood have increased their popularity as structural materials thank to their outstanding environmental performance, competitive price, mechanical properties, and relatively easy handling
Evidence exists that structural wood can retain its strength through many centuries [2], it is very sensitive to the variable temperature (T) and moisture content (MC) which may lead to the material degradation and loss of its structural performance [3]
The combination of the sensor-based monitoring and numerical model presented in the previous sections, allowed analysing the hygro-thermal response of the uncoated Stress-laminated timber decks (SLTDs) of Sørliveien Bridge in Norway and the thick painted SLTD of Tapiola Bridge in Finland

Summary

Introduction

Timber and engineered wood have increased their popularity as structural materials thank to their outstanding environmental performance, competitive price, mechanical properties, and relatively easy handling. Stress-laminated timber decks (SLTDs) are composed of wood lamellas placed longitudinally between the supports of the bridge and compressed together with preloaded steel bars in the transverse direction (see [4] and the related references). This technology was developed in Canada in 1976 to replace nail-laminated wooden decks, which delaminated under cyclic loading and moisture variation. The greatest advantage of laminated decks is that they form a stiff and solid base for the pavement, and can redistribute the external loads to their supports This effect is due to the prestressing action of the high-strength steel bars that squeeze the wooden lamellas together. The bar force, measured by using load cells, is typically from 89 to 356 kN [4]

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Discussion

Conclusion